Antennas that include a dielectric radiator that is excited using a series of polarization devices are known in the art. Such antennas are referred to herein as “polarization current antennas.” An example of such a polarization current antenna is disclosed in European Patent No. 1112578 titled “Apparatus for Generating Focused Electromagnetic Radiation,” filed on Sep. 6, 1999. Each polarization device may comprise, for example, a pair of electrodes that are positioned on opposite sides of a ring-shaped dielectric radiator. The dielectric radiator may be a continuous dielectric element, and the electrode pairs may be positioned side-by-side on inner and outer sides thereof. Each pair of electrodes and the portion of the dielectric radiator therebetween forms a “polarization element” of the polarization current antenna.
The above-described polarization current antenna may operate as follows. When a voltage is applied across one of the electrode pairs, an electric field is generated across the portion of the dielectric radiator therebetween. The electric field generates a displacement current within the dielectric radiator. This displacement current may be referred to as a “volume polarization current” because the current is generated by polarizing the portion of the dielectric material that is between the electrode pair throughout its volume. The generated volume polarization current emits electromagnetic radiation. A volume polarization current distribution pattern may be generated in the dielectric radiator by applying different voltages across multiple of the electrode pairs. Moreover, this volume polarization current distribution pattern may be caused to propagate within the dielectric radiator by appropriate sequencing of the energization of the electrode pairs. One example of a moving volume polarization current distribution pattern is a polarization current wave such as, for example, a sinusoidal polarization current wave that propagates through the dielectric radiator. This polarization current wave can be made to propagate through the dielectric radiator in a direction orthogonal to a vector extending between the electrodes of an electrode pair. Polarization current antennas that have dielectric radiators that are driven by individual amplifiers are known in the art. See U.S. Pat. No. 8,125,385, titled “Apparatus and Methods for Phase Fronts Based on Superluminal Polarization Current,” filed Aug. 13, 2008, which is incorporated herein by reference. Polarization current antennas that are driven by a passive feed network are also known in the art. See International Patent Publication No. WO/2014/100008, which is also incorporated herein by reference. Polarization current antennas differ from conventional antennas in that their emission of electromagnetic radiation arises from a polarization current rather than a conduction or convection electric current.
Polarization current antennas that generate polarization current waves that move faster than the speed of light in a vacuum have been experimentally realized. One example of such a polarization current antenna that has already been constructed and tested functions by generating a rotating polarization current wave in a dielectric radiator that is implemented as a ring-shaped block of dielectric material. By phase-controlled excitation of the voltages that are applied to electrodes that surround the dielectric radiator, a volume polarization current can be generated that has a moving distribution pattern (i.e., a polarization current wave that travels along the dielectric radiator) that changes faster than the speed of light and exhibits centripetal acceleration. See, e.g., U.S. Patent Publication No. 2006/0192504 (“the '504 publication”); see also, U.S. patent application Ser. No. 13/368,200, titled “Superluminal Antenna” filed on Feb. 7, 2012, the disclosures of each of which are incorporated herein by reference. It should be noted that while the polarization current wave travels faster than the speed of light, the movements of the underlying charged particles that create the polarization current wave are subluminal.
FIG. 1 is a perspective view of the polarization current antenna 1 that is disclosed in the '504 publication. As shown in FIG. 1, the polarization current antenna 1 includes a ring-shaped dielectric radiator 2 that has a plurality of inner electrodes 4 that are disposed on an inner surface of the ring-shaped dielectric radiator 2 and a plurality of outer electrodes 6 that are disposed on an outer surface of the ring-shaped dielectric radiator 2. The ring-shaped dielectric radiator 2 circles an axis of rotation z. The polarization current antenna 1 of FIG. 1 produces tightly-focused packets of electromagnetic radiation that are fundamentally different from the emissions of conventional antennas.
Polarization current antennas that generate polarization current waves that move faster than the speed of light can make contributions at multiple “retarded times” to a signal received instantaneously at a location remote from the polarization current antenna. The location where the electromagnetic radiation is received may be referred to herein as an “observation point,” and each “retarded time” refers to the earlier time at which a specific portion of the electromagnetic radiation that is received at the observation point at the observation time was generated by the volume polarization current. The contributions to the electromagnetic radiation made by the volume elements of the polarization current that approach the observation point, along the radiation direction, with the speed of light and zero acceleration at the retarded time, may coalesce and give rise to a focusing of the received waves in the time domain. In other words, waves of electromagnetic radiation that were generated by a volume element of the polarization current at different points in time can arrive at the same time at the observation point. The interval of time during which a particular set of electromagnetic waves is received at the observation point is considerably shorter than the interval of time during which the same set of electromagnetic waves is emitted by the polarization current antenna. As a result, part of the electromagnetic radiation emitted by the polarization current antenna possesses an intensity that decays non-spherically with a distance d from the antenna as 1/d2−α with 0<α<1 rather than as the conventional inverse square law, 1/d2. This does not contravene the physical law of conservation of energy. The constructively interfering waves from the particular set of volume elements of the polarization current that are responsible for the non-spherically decaying signal at a given observation point constitute a radiation beam for which the time-averaged value of the temporal rate of change of energy density is always negative. For this non-spherically decaying radiation, the flux of energy into a closed region (e.g., into the volume bounded by two large spheres centered on the source) is smaller than the flux of energy out of it because the amount of energy contained within that region decreases with time. (The area subtended by the beam increases as d2, so that the flux of energy increases with distance as dα across all cross sections of the beam.) In that it consists of caustics and so is constantly dispersed and reconstructed out of other electromagnetic waves, the beam in question has temporal characteristics radically different from those of a conventional beam of electromagnetic radiation.